Luminescent materials are often used to detect faults, such as leaks or stress fractures. Such luminescent materials can be applied to a body in many ways. Two common ways include using magnetic particles and liquid penetrants.
Magnetic particles such as iron filings are mixed with fluorescent materials and applied to a body. The particles and fluorescent materials form distinctive patterns depending upon the characteristics of the body. For example, fluorescent dyes combined with iron filings can be used to detect faults such as stress fractures. The fluorescent material is applied to a body to be tested in such a way as to highlight a fault in the body when the material is illuminated by shining a lamp emitting light of a particular wavelength on the body. The combined iron filings and fluorescent dye are attracted to the fault and the dye emits visible light when illuminated by incident light of an appropriate wavelength. For example, metal in aircraft components will act differently in the presence of magnetic fields and thus cause distinctive patterns of magnetic particles applied to the components, depending upon the existence of faults within the components. Such faults are typically caused by previous stresses.
Liquid penetrants are also mixed with fluorescent materials to reveal faults by penetrating cracks or other faults in a body. For example, a luminescent material in the nature of a fluorescent dye is injected or poured into a component or system. Where a leak occurs the dye may escape from the system. Shining a light of appropriate wavelength (typically ultraviolet or near ultraviolet) on the system will cause the dye to fluoresce in the area of the leak. The existence and location of a leak or leaks are then evident.
Leaks in various liquid and vapor circulating systems, such as air conditioners, may be discovered by including a dye with the circulating liquid or vapor. The dye used is preferably capable of fluorescing when exposed to an ultraviolet or near ultraviolet (“UV”) spot light or flood light. These lights typically emit light having a wavelength in the 385 to 485 nanometer range. As described above, leaks may be detected by illuminating the system with such a light to fluoresce any dye escaping from the system. The dye may be injected, poured or otherwise introduced into the system. A leak may be detected as the liquid or vapor, which includes a fluorescing dye, escapes from the system or apparatus, for example, through a hole or crack, or at a seal or other connection that is failing. The fluorescence of the dye may then be detected by visual inspection using the near UV spot light or flood light to cause the dye to fluoresce.
Typically, light energy or radiation that has its peak output in a wavelength range of 385 to 465 nanometers will cause a luminescent material such as a fluorescent dye to fluoresce. Light falling outside of this range may tend to interfere with detection of the fluorescing dye. Accordingly, to improve detection, it may be preferable to reduce the presence of any remaining visible light, which typically has a wavelength in the 480 and 700 nanometer range. Reduction of interfering visible light may be achieved by placing a filter in the path of the emitted light.
Near UV spot lights or flood lights typically contain incandescent lamps, such as tungsten halogen lamps, along with a filter which inhibits transmission of light energy (or radiation) outside of the 385 to 465 nanometer range. These lights may be flashlight or lantern type devices that emit a beam of near UV energy. They can operate while powered by a self-contained battery or an electrical outlet. The incandescent light source, however, is not generally considered to be an efficient means of producing near UV energy because over 80% of the energy is typically emitted as infrared light or heat, and only about one percent of the energy emitted is near UV energy. A usable beam of energy is obtained because these lamps produce a narrow, intense beam of light from a “point source” (i.e., the energy emits from a concentrated area of the light source).
When a flood light for close inspection is desired, a black light blue (“BLB”) type fluorescent lamp whose energy output is limited to the near UV range may be used. A miniature or compact version of such a lamp may be convenient for close inspection of difficult to access parts of the system being inspected. It is desirable to be able to bring the lamp in to close proximity with the fault. This is often difficult to achieve, even with miniature versions of such fluorescent lamps, when used in the tight spaces typically available when working around machinery and equipment.
Use of fluorescent lamps generally reduces the need for a filter to reduce the visible light emitted. Since these lamps are “area sources” (i.e., the energy emits from a relatively large area of the light source) and not point sources, they can generally only produce a floodlight beam which can be difficult to focus on a particular area of an inspected system. In particular, fluorescent lamps tend to generate a low intensity of incident ultraviolet radiation. However, they are generally advantageous in that they can efficiently produce near UV energy. Typical lamps are 4 to 13 watts and they can operate using a ballast powered by batteries or line voltage.
Based on the foregoing, alternative methods and apparatus for using lamps and dyes to locate faults and defects in machinery and other equipment is desirable.